The present invention relates to a fixing heater used for fixing toner image in a copying machine, for example, and also relates to a method of manufacturing the same.
In a conventional technology, a fixing heater used for fixing toner image in a copying machine, for example, is produced by applying a paste of, for example, a silver-palladium alloy powder on the surface of an elongated substrate such as ceramics as shown in FIG. 9 and then firing the applied paste.
For the heat fixing of the toner image, a uniform temperature application is generally required such as of 200.degree. C. with less allowance of about 10.degree. C. In this type of fixing heater, it is necessary that a resistance value of a film-like heat generating member 2 is adjusted to fall within a predetermined range so as to obtain a constant heat generation rate when a predetermined level of electrical current is applied. In the conventional technology, such adjustment of the resistance value has been done by varying a sheet resistance value of the heat generating member 2 by varying the amount of the conductive paste constituting the material of the heat generating member 2 and being printed to a substrate 1, i.e. the size of the heat generating member or by selecting the material of the conductive paste.
However, in this conventional technology, the resistance adjustment method has to be performed before the firing for the print of the heat generating member. Thus, it has not been allowed to effect a fine readjustment after the firing, which makes it difficult to obtain a desired resistance value and, hence, causes a large variation or fluctuation of a generated temperature of a fixing heater as a product.
In a conventional technology, there has been also proposed a method in which, as shown in FIG. 10A, a resistor is printed in a manner used in ordinary hybrid ICs (integrated circuits) and the resistor as the heat resisting member 2 is then subjected to triming so as to provide a key-like shape by using a laser, for example. However, a mere application of the laser triming treatment to the fixing heater produces a temperature distribution as shown in FIG. 10B in which heat generation is locally increased at the trimmed portion, resulting in a cause of non-uniform fixing. Thus, such conventional technology is not available for fixing the toner image in a copying machine.